Innovations in Enhanced Flooded Lead-Acid Batteries

© 2016 Daramic, LLC. ALL RIGHTS RESERVED

Innovations in Enhanced Flooded Lead-Acid Batteries

J. KEVIN WHEAR

VP Technology

© 2016 Daramic, LLC. ALL RIGHTS RESERVED 2

Agenda

Market Overview

Lead–Acid Battery Needs

Innovation in Enhanced Flooded Lead-Acid Batteries

1. Improving power output

2. Improving cycling in Partial State of Charge (PSoC)

3. Improving dynamic charge acceptance

Conclusion


Drivers

Environmental drivers creating new battery demands for

OEMs & Suppliers

Start-stop vehicles require more robust lead-acid battery designs to meet changing conditions

• Environmental/ Regulatory Compliance

1. CO2 reduction

2. Fuel savings

• Consumer economics

• Engine technology moving away from

combustion only engine, focused on Start-

Stop in response to end market drivers

• Start-stop vehicles will account for >53

million new vehicles sold annually by 2020

Battery Manufacturers

• Combustion engine battery -- low discharge

frequency and always fully charged

• Start-stop requires battery to always be in

partial state of charge (PSoC)

• Two choices today: Enhanced Flooded

Battery (EFB) or AGM

Start-stop Battery

Depth of Discharge

End Markets Auto Manufacturers (OEMs)

Source: Navigant Research; Internal Analysis

Electric

Start-Stop

Combustion

Engine

# of vehicles sold

System Development

Unit: thousand

Suppliers


Technical gaps between EFB & AGM – two primary choices

in start-stop systems

Relative to AGM, Enhanced Flooded Lead-acid batteries must maintain key benefits, while meeting needs in power output, cycling in PSoC & dynamic charge acceptance

Technical / commercial needs

Power output (cranking)

Cycling in PSoC

Dynamic charge acceptance

Short protection to deep discharge

Endurance at high temperature

Lower system cost

Poor Excellent

Source: The comparison is based on various test results including Cycling (50%

DoD), PSoC Cycling (17.5% DoD), Charge Acceptance, SAB test with thermal

isolation, etc.



Power Output Cycling in PSoCDynamic Charge

Acceptance

• Increase power output by lowering separator resistance


Improving power output

Improved separator design to minimize voltage drop during restart

Voltage drops on every restart – upwards

of 70 times during an urban commute

If minimum voltage level is crossed:

• Lights Dim

• Radio turns off

• Loss of GPS

Poor vehicle

perception

Actions Issues

Minimize engine off Higher emissions, higher fuel consumption

Increase battery size More weight, higher cost

Larger cables / battery close to starter More weight, higher cost, engine redesign

Thinner separator (< 200 micron) with Lower ER Increased chance of separator failure / battery failure

Lower ER separator (> 200 micron) New separator design

Volt

age

Time

Motorway Urban (Start/Stop)

Minimum Voltage Level

Motorway

1

Typical Start-Stop Voltage Profile

Options to Mitigate Dropping Below Minimum Voltage Level

2

1

2



Instead of lowering ER by reducing backweb, another solution is needed without additional risks for OEMs

0

10

20

30

40

50

60

70

100 120 140 160 180 200 220 240 260

Separa

tor

Ele

ctr

ical Resi

stance

(mohm

s-cm

2)

Backweb Thickness (microns)

Solution 1: 25% Reduction in ER by lowering backweb thickness

As backweb thickness is

reduced, so is ER

Risk Factors:

1. More puncture

shorts Battery

failures

2. Difficult to envelope

manufacturing cost

Typical Replacement Typical OEM

+25%

150

microns


0

10

20

30

40

50

60

70

100 120 140 160 180 200 220 240 260

Separa

tor

Ele

ctr

ical Resi

stance

(mohm

s-cm

2)

Backweb Thickness (microns)


Lower separator resistance can be achieved with an advanced modified separator design

+25%

Standard PE Separator

New PE Separator*

Solution 2: 25% Reduction in ER by increasing separator porosity

• Replace current

separator with a 6%

more porous separator

• +25% Reduction in ER

by product

modification

• Robust solution,

thicker backweb is

maintained – reduced

shorts, punctures,

increased durability

Typical OEM

*Daramic Proprietary IP


New PE Separator with Lower ER

At higher porosity, mechanical properties can be maintained with shish-kebab polymer structure

K Wang, F Chen, Q Zhang,

Q Fu Polymer. 2008

New PE Structure*

Characteristic Standard PE Separator New PE Structure* Change

Porosity (%) 60.1 63.9

Electrical Resistance

(mohms-cm2)65 44

Puncture Resistance (N) 13.5 12.1 -

CMD Elongation (%) 350 375

Oxidation Resistance

(Perox 80)

@20 Hours (%) 252 @20 Hours (%) 305

@40 Hours (%) 176 @40 Hours (%) 215

Standard PE Network

Standard PE Structure

Shish-Kebab

Polymer Network

Improves Strength

(e.g. Puncture

Resistance)

Silica Clusters

Kebab

Shish



Cold start battery test results with various separators

Lower separator resistance can bring lower voltage drop & prolong discharge time

Battery Size: L2; Type: Enhanced Flooded Battery (EFB)

Step 1: (V) 850A for 10 Seconds

0.15V+44%

Daramic’s New PE Separator shows longer duration to minimum voltage, especially in cold testing environments

Daramic’s New PE Separator reduces the impact of minimum voltage threshold being crossed, while in start-stop mode

Other testing validation:

25% lower separator ER resulted in ~4% lower battery resistance

Lower battery resistance yields more power by both EN & SAE tests

Step 2: (seconds) 510A to 6 Volts


**



Acceptance

• Modified Separator to prevent acid stratification and improve cycling



Preventing Acid Stratification – Current Solutions

Two options to prevent acid stratification have definite cost implications, up to $10/battery

AGM separators have:

1) High Internal Surface

Area (> 1.0 m2/g)

2) High Porosity (>90%)

Acid is immobilized which

delays the onset of acid

stratification

Manufacturing, Design, R&D

Cost: ~$10/battery

A Weir System is a

mechanical component that

takes advantage of the

vehicle stopping / starting

& resultant sloshing

Transfers weak acid from

the top to mix with strong

acid at the bottom

Device & Assembly Cost:

~$1/battery

SEM of an AGM Separator

US Patent Application 2012/0214032

CostSolutionProperties


Computational Fluid Dynamics (CFD) predicts fluid

behavior inside battery

Positive enveloped plate shows minimum acid mixing due to energy associated with accelerating & braking

Simulation Conditions• Time: 60 seconds; Distance: 2

feet forward, 2 feet backward;

Number of cycles: 30

• Positive enveloped & standard

profile

Battery

head space,

still only

water

Separator Ribs acting as

solid baffles which

contain lateral movement

of acid

Bottom half of

the battery,

concentrated

acid

Slight mixing at

the interface &

more on the

edges

Slightly more

acid mixing

outside of

positive

enveloped plate

Concentrated Acid

(35 wt.%)

Pure Water (0 %

Acid)

Motion

1. Vehicle motion promotes mixing in the

battery head space

2. No mixing is occurring between the

plates

1

2Top of

the

plates

Minimum mixing after start-stop motion Computational Fluid Dynamics (CFD)

1

2


Uniformity index is to be optimized

Start-stop motion yields marginal (5%) improvement in acid mixing

Uniformity Index – Describes the distribution of a acid within the battery case. When the acid is distributed equally,

the resulting number is 1.0

CFD modeling of acid mixing associated

Advection

Diffusion

Turbulence

𝑼𝒏𝒊𝒇𝒐𝒓𝒎𝒊𝒕𝒚 𝑰𝒏𝒅𝒆𝒙 𝒐𝒇 ∅ = 𝟏 −

𝒄

∅𝒄− ∅ 𝑽𝒄

𝟐 ∅

𝒄

𝑽𝒄

0.34

Bett

er

Mix

ing

5%

Approaching asymptotic limit after 60

seconds of motion∅ Average volume of acid

∅𝑐Volume of acid in selected

cell (e.g. pixel)

𝑉𝑐Volume in the selected

cell

CNumber of cells (+10

million)

Starting point with no movement, uniformity index @ 0.32


Serrated Rib to allow for horizontal acid movement

Serrated rib profile combined with start-stop motion improves acid mixing by 10%

Solid Rib Profile(Volume Uniformity @ 0.34)

Serrated Rib Profile*(Volume Uniformity @ 0.36)

Expanded

Mixing

Interface

Localized

Mixing

Occurring

Serrated Rib Profile

Mixing Uniformity Scorecard

Start-stop motion +5%

Serrated rib +5%

Total +10%



Serrated Rib plus Negative Envelope

Serrated rib profile & negative enveloping can improve acid mixing by 18%

Serrated Rib*(Volume Uniformity @ 0.36)

Serrated Rib* &

Negative Envelop

(Volume Uniformity @ 0.39)

1) Negative enveloping allows greater

mixing of acid with bulk or acid in

the domain region

2) Serrated rib allows acid to move

across the surface of the plate

Substantial movement of

concentrated acid into dilute

region



Serrated rib +5%

Change to negative

envelope+8%

Total +18%

Positive PlateNegative Plate

Fluid

Domain

Serrated

Separator



Profile Design Optimization

Seek optimized serration design to improve acid mixing

Approach 1: Break the rib to allow acid mixing

Approach 2: Optimize serration design (angle, column spacing & height) to optimize mixing

Approach 1:

Serrated Rib* Approach 2:

Concept Design*

Goal: Convert start-stop motion into vertical acid mixing



Optimized Serrated Rib Design

Optimized serrated rib profile yields added benefit to acid mixing

Serrated Rib* &

Negative Envelop

(Volume Uniformity @ 0.39)

Optimize Rib Profile*

Negative Envelop(Volume Uniformity @ 0.41)



Serrated rib +5%

Change to negative envelope +8%

Optimized serrated profile* +5%

Total +23%

Substantial improvement in

acid mixing due to:

1) Optimized Profile

2) Negative Envelop

Water (Acid wt 0%)

High Concentration Acid

Column is expanding higher

into the vertical space

*Daramic Proprietary IPConcentrated Acid

(Acid wt 35 %)


Bett

er

Mix

ing

Summary of CFD Work

Optimized profile design & negative enveloping brings improvement to acid mixing & reduces stratification and close the technical gap with AGM

Started with worst case scenario

– 100% acid stratification

– Limited motion (e.g. 60 seconds)

Uniformly mixed acid

– Provide better utilization of electrodes to receive

energy and to provide energy

– Prevent dead zones or sulfated regions on the

electrode that are prone to shedding & thus improve

PSoC

Solid Rib Serrated Rib* Serrated Rib*

& Neg EnvOptimized Rib*

& Neg Env

CFD = Computational Fluid Dynamics




Acceptance

• Preventing acid stratification in the battery, while adding carbon active material

will improve battery charge acceptance



Improve charge acceptance by preventing acid stratification

Preventing acid stratification will maintain larger functional area & prevent concentration of sulfate crystals

Step 1: Charging in PSoC

H2SO4 generates upon charging &

collects toward the bottom

rendering only a portion of the

electrode functional

Upon discharge PbSO4 is generated on

electrode surface in the functional

area

Crystalline layer of PbSO4 is

generated deep into the electrode

ultimately rendering inoperable

Reduction proportional to

functional area (50%)

Reduction proportional to functional

area (50%) & time to reduce large

sulfate crystals

Impact Impact

Sulfate Crystals

Step 2: Discharging in PSoC Step 3: Continual Discharge in PSoC

Reduction proportional to functional

area (50%) & time to reduce large

sulfate crystals

Impact


0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Control Separator Modified Separator

Cumulative Water Loss

Carbon Sb Strap Process Acid Pb

Improve charge acceptance with carbon added to the NAM

More carbon can be added as water loss is reduced with a modified separator

Potential Rate Limiting Factors Means of Mitigation

Poor conductance of electrons to lead

sulfate layer exposed to bulk

electrolyte

Addition of conductive materials

(e.g. carbon)

Large lead sulfate crystal with limited

surface to be reduced

Add nucleation sites (e.g. Carbon) to

maintain smaller lead sulfate crystals

-1.8 -1.6 -1.4 -1.2 -1.0 -0.8 -0.60.10

0.08

0.06

0.04

0.02

0.00

-0.02

-0.04

-0.06

Direction of Scan

Curr

ent

(A)

Voltage (V vs. MSE)

100 ppm Sb+3

added

No Sb added

Negative Sweep of CV Showing Reduction Reactions

0.57 cm2 Pb Electrode in SG = 1.28 Acid

H2 Evolution

-1.6 -1.5 -1.4 -1.3 -1.2 -1.10.04

0.03

0.02

0.01

0.00

-0.01

IEvol

with SB

Cu

rre

nt (A

)

Voltage (V vs. MSE)

IEvol

no SB

Carbon improves charge acceptance…

…while increasing water loss

Decreasing water loss via separator modifications

can allow for greater concentrations of carbon &

improved charge acceptance

Required OEM Spec

Wate

r Loss

(g/am

p-h

r)

~25%

Reduction


Highly engineered modifications can improve EFB to

performance level of AGM

Separator designs can yield improvements to the enhanced flooded battery performance

Technical / commercial needs

Power output (cranking) Low ER Separator

Cycling in PSoC Passive Acid Mixing

Dynamic charge acceptancePassive Acid Mixing,

Lower Water Loss

Short protection to deep dischargeMicro-Porous Polymer

Structure

Endurance at high temperature Excess Electrolyte

Lower system costFaster Assembly &

Fewer Components

Poor Excellent

Source: The comparison is based on various test results including Cycling (50%

DoD), PSoC Cycling (17.5% DoD), Charge Acceptance, SAB test with thermal

isolation, etc.

Solutions VRLA-AGMEFB

w/o solutionsEFB

with solutions


Thank you!

Automotive

Innovations in Enhanced Flooded Lead-Acid Batteries